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Electrochemical impedance spectroscopy (EIS) has been used to study adsorption from solution on metallic substrates and corrosion mechanism. In this present study the interaction between plain steel (S235JRG2, according to Polish standard PN-EN 10025-2:2005) and low temperature ionic liquids was studied by means of EIS. A series of 1-alkyl-3-methylimidazolium tetrafluoroborates where alkyl=butyl, hexyl or octyl was selected as representative ionic liquids. In addition to pure ionic liquids, the samples contaminated with water and/or chlorides were studied. Water and chlorides are typical impurities in commercial ionic liquids. The corrosion rate decreases with the length of substituent in the imidazolium ring, and increases with the temperature (range 25-50 oC). The presence of impurities enhances the adsorption rate, and water and chlorides present simultaneously have a synergic effect. The enhanced corrosion rate in the presence of water and/or chlorides is due to low resistivity of the layer of corrosion products as compared with the layers formed in pure ionic liquids. The elementary composition of the corrosion products is also affected by the impurities, but in all studies samples the corrosion products contain oxygen, and all constituents of the ionic liquids.
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